In a message dated 7/30/2013 1:36:12 P.M. Eastern Daylight Time,
Lehanover@aol.com writes:
The rotary has three features that make for a poor idle
compared to a piston engine.
Heat of compression.
The rise in chamber temperature
caused by compressing the fuel/air mixture.
The rotary has poor heat of compression because of the large surface are
of the chamber, and much of the chamber surface is cooled. Low heat of
compression allows fuel droplets to condense on the chamber surfaces and the
engine sees this as a mixture that is too lean to light.
Compression leakage:
The rotor face has many end
gaps through which it leaks compression.
For example, on NA rotaries I
gap the side seal to corner seal at zero. So long as the combination of two side
seals and the joining corner seal pop back up when depressed and released, that
is sufficient. The zero gap will become a measurable gap shortly after break in.
Overly wide end gaps lead to leakage of compression, and that leads to lowered
heat of compression as above.
Effective compression ratio:
At idle and near idle, the amount of air allowed into the engine is
minimal. So the computer limits the injection pulse width accordingly.So the
cylinder filling is minimal, and so heat of compression is minimal.
So, if the same amount of cylinder filling is used. The rotor with the
higher compression ratio will generate fewer misses and a smoother idle. Because
for a fixed cylinder filling number, the higher compression rotor produces
the highest heat of compression.
Higher heat of compression means better fuel vaporization and a more
thorough burn.
A misfire is an event wherein a dose or part of a dose of mixture was not
lighted at or near the correct time during the cycle.
A misfire that involves no burned mixture is a noticeable event, in that
the engine will be out of balance for that cycle. The engine will wiggle in its
mount. A misfire that involves a trailing plug will not be noticed at or near
idle. A misfire that involves the leading plug can be noticed by the very
attentive.
A popping sound in the headers or exhaust in general with no engine wiggle
is more likely a small air leak in the header, that allows oxygen to mix in the
header with some as yet unburned fuel. The popping is this mixture igniting.
Very likely to be experienced on long closed throttle descents.
A misfire at higher throttle settings and full power, will be very
noticeable, as an unlighted charge between two lighted charges will produce
quite an imbalance jerk in the engine, and the mixture from the misfire
will light in the header right outside the engine. So you get a jerk and a loud
change in engine tone.
This does not damage the engine, but can damage the exhaust system and,
or, ruin a muffler. As has been seen, a damaged muffler can stop an engine
or reduce it's power out put to useless levels.
Lynn E. Hanover